Electrical cables are used to connect together a variety of pieces of electrical equipment. In both domestic and industrial usage, it is common for fixed wiring cables to be inserted through an opening or hole in the wall of an enclosure, in which the cable terminates and is connected to electrical devices contained within the enclosure. Commonly, the enclosure can comprise an outlet box, in which an electrical receptacle, switch, etc., is mounted. It is desirable that the cable be clamped to prevent any mechanical loads being applied to the actual electrical connections and the opening should be substantially closed.
Electrical codes commonly require the cable to be clamped and the opening at least partially closed after insertion of the cable. At least for outlet boxes, and for a number of other enclosures, it is common to provide a number of knockouts, i.e. disc-shaped portions of the enclosure or housing, which are partially precut, to enable easy removal to form an opening. This provides a great degree of flexibility, since an end user can form the number of openings required, in the sides of the enclosure that are most advantageous.
Once the opening has been formed, it is then necessary to provide some sort of a clamp. Such a clamp can be a separate element that is secured to the housing, as by having two elements that are screwed together, in the wall of the housing. This is relatively inconvenient and time consuming.
More recently, single unit, plastic strain relief cable connector clamps, including a self-locking mechanism have become widely used. These have the advantage that they are relatively cheap and simple to make, since they are formed as a single unit component, moulded in plastic. Installation is also relatively quick and simple. The cable clamp is essentially tubular with a slit along one side, to enable it to be squeezed, for insertion into the knockout or opening of an enclosure. It then resiliently returns to its original shape, and is provided with protruding ribs to lock it in the opening.
Within the cable connector, there is a clamping element, which simply resiliently deflects as a cable is inserted. Its free end is resiliently biased against the cable sheath, with the intention that it will engage the cable, to prevent the cable being withdrawn. Thus, no separate clamping action is required.
However, in order to accommodate a wide variety of different cable sizes, it is desirable for the clamp to have a larger clamping range. Such a known design, because of its geometry, provides a substantially higher initial clamping pressure or load for a small cable, as opposed to a large cable. For a large cable, the clamping element is at a poor angle to provide a significant clamping force.
An additional problem is that electrical codes commonly stipulate that openings in connectors should be practically closed after the cable has been inserted. In this known design, the clamping element is largely circular. For larger cables, when the clamping element is deflected, it interferes with the sides of the connector clamp, which in turn interferes with insertion of the cable and the clamping action.